Mir-21 Regulation of MARCKS Protein and Mucin Secretion in Airway Epithelial Cells

W Randall Lampe,Joungjoa Park,Qi Yin,Shijing Fang,Anne L Crews,Kenneth B Adler

doi:10.4236/ojrd.2013.32014

Abstract

Hypersecretion of mucus characterizes many inflammatory airway diseases, including asthma, chronic bronchitis, and cystic fibrosis. Excess mucus causes airway obstruction, reduces pulmonary function, and can lead to increased morbidity and mortality. MicroRNAs are small non-coding pieces of RNA which regulate other genes by binding to a complementary sequence in the target mRNA. The microRNA miR-21 is upregulated in many inflammatory conditions and, interestingly, miR-21 has been shown to target the mRNA of Myristoylated Alanine-Rich C Kinase Substrate (MARCKS), a protein that is an important regulator of airway mucin (the solid component of mucus) secretion. In these studies, we determined that exposure of primary, well-differentiated, normal human bronchial epithelial (NHBE) cells to the pro-inflammatory stimulus lipopolysaccharide (LPS) increased expression of both miR-21 and MARCKS in a time-dependent manner. To investigate whether miR-21 regulation of MARCKS played a role in mucin secretion, two separate airway epithelial cell lines, HBE1 (papilloma virus transformed) and NCI-H292 (mucodepidermoid derived) were utilized, since manipulation of miR-21 is performed via transfection of commercially-available miR-21 inhibitors and mimics/activators. Treatment of HBE1 cells with LPS caused concentration-dependent increases in expression of both miR-21 and MARCKS mRNA and protein. The miR-21 inhibitor effectively reduced levels of miR-21 in the cells, coincident with an increase in MARCKS mRNA expression over time as well as enhanced mucin secretion, while the miR-21 mimic/activator increased levels of miR-21, which coincided with a decrease in expression of MARCKS and a decrease in mucin secretion. These results suggest that miR-21 is increased in airway epithelial cells following exposure to LPS, and that miR-21 downregulates expression of MARCKS, which may decrease mucin secretion by the cells. Thus, miR-21 may act as a negative feedback regulator of mucin secretion in airway epithelial cells, and may do so, at least in part, by downregulating expression of MARCKS.

Highlights

Hypersecretion of mucus characterizes many inflammatory airway diseases including asthma, chronic bronchitis, and cystic fibrosis
The microRNA miR-21 is upregulated in many inflammatory conditions and, interestingly, miR-21 has been shown to target the mRNA of Myristoylated Alanine-Rich C Kinase Substrate (MARCKS), a protein that is an important regulator of airway mucin secretion
To investigate whether miR-21 regulation of MARCKS played a role in mucin secretion, two separate airway epithelial cell lines, HBE1 and NCI-H292 were utilized, since manipulation of miR-21 is performed via transfection of commercially-available miR-21 inhibitors and mimics/activators

Summary

Introduction

Hypersecretion of mucus characterizes many inflammatory airway diseases including asthma, chronic bronchitis, and cystic fibrosis. Excessive mucus can obstruct airways, inhibit respiration, increase susceptibility to infection, and lead to increased morbidity and mortality. Mucus is a gel made up of water and mucins (large complex glycoproteins) that are post-translationally modified by myristoylation, glycosylation and/or phosphorylation. Mucins provide mucus with its viscosity and elasticity [1]. At least 20 different mucins have been discovered in humans, 11 of which have been identified in the lungs. MUC5AC and MUC5B are the most prominent types in the airways [2].

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Conclusion